The goal of mirroring is to copy data from one location to another, thereby resulting in two copies of the same data, with the premise that if one copy is destroyed, the other copy is still available, and hence, there is no loss of valuable data. In order to provide the fastest and most reliable way to save the data, dual disk array controllers should be utilized. These disk array controllers employ a data cache, where the user's data is initially written prior to finally being written to a physical medium such as a disk drive.
For a fault tolerant system, the dual controllers maintain a copy of each other's data caches, such that if one controller fails to write the cached data to the physical medium, the other controller will use its copy of the data to write it to the physical medium. One of the primary problems associated with mirroring is that it takes some additional time to perform the copy operation. The additional time spent making this copy reduces the amount of time, which can be spent on other data storage and retrieval operations. Performance suffers when mirroring is being performed, possibly by as much as 30 to 40 percent. Clearly, this performance degradation is undesirable.
The present inventor has therefore concluded that a need exists for improved methods and systems for enhancing the performance of data mirroring operations. The present inventor believes that this can be achieved through a fundamental rearrangement of traditional mirroring approaches, including new techniques for prioritizing and queuing, which are disclosed in further detail herein.